Electrostatic coating apparatus



y 29, 1952 w. R. BLOOD ET AL ELECTROSTATIC COATING APPARATUS Filed Feb.1 1950 I 1 I I "I Invewbovs:

e .,w mm m m m/% /IT R m. A a ks W 6 G In m T 'J b 6 H Patented July 29,1952 ELECTROSTATIC COATING APPA ATUS" Q. 1

. iwwalter' Roy. Blood and James- Willi'a'in Moorer Rugby;'England,assignors to General Electric Company, acorporation of New York gApplication February 1, 1950, Serial No. 141,705

In England February 1, 1949 This invention relates to the formation ofthe. luminescent screen or layer of a fluorescent-lamp by theelectrostatic precipitation of powdered luminescentmaterialont'ozthe-surface which is to sustain thescreen;

In. the carrying. out ofsthis process; powder is introduced into thecontainer which is toform the envelope of the fluorescent-lamp in theform of a smoke and the-powder particlesin the smoke are ionized bythe-application of a high potentialbetween any electrodepositionedwithin the containerand the container wall.

Iii-order thatauniiorm depositof the particles be obtained, it. isnecessary that the part of the wall of the container which is beingcoated be maintained at a substantially uniform potential.

According to" the" invention, the substantially uniform potential isobtained by providing an electrode outside the wan of the containerbeing coated with a plurality f point-like extensions toward said wall,the point-like extensions being uniformly distributed over the portionof the wall on which coating is being effected:

The uniform distribution .of'the point-likteextensions over thesurfaceof a tubular container may be obtained by employing a conductingsleevesurrounding the container wall and uniformly distributing thepoint-likeextensionsifrom the 'innersuriace of the sleev;.' of byemploying an electrode of limited extent axially and/or transversely ofthe container and rapidly moving the electrode axially of and/orrotating it around the container so as to cause the point-likeextensions from it to be eiiectively distributed over the portion of thesurface being coated. We preier to use an electrode in the form of astirrup, the axes of which extend parallel to the axis of the containerand are provided with the extensions, the stirrup being rotated rapidlyaround the container.

The point-like extensions may be constituted by pointed wires, e. g.,phonograph needles, the tips of which are spaced a short distance fromthe wall.

It will be understood that in carrying out the electrostaticprecipitation process smoke is introduced into the container so that itdrifts along the container, which is assumed to be tubular, theproduction and application of the smoke being arranged to this end. Aninner electrode is arranged within the container and is moved axiallythereof in the path of the advancing body of smoke. A difference ofpotential is maintained between the inner electrode and the wall of thecontainer by applying a high D, C. potential bewhich is earthed'. Theouter'electrod'e i s moved with the inner electrode and 'the powder isuniiormly electrostatically precipitated from the.

smoke onto th'e'i nner surface 01 the container. The tube to be coatedis preferably mounted with its longitudinal axis vertical' and is heldin this position by meanso'f aclip-whi-ch is mounted on a" standardextending alongside the-tube,- and canbe' moved along the standardtoenable the tube to be inserted in positionfor coating",- and removed.after coating. The outer electrodeis then rotatably mountedon a carriagemovable along the standard.

For afurther understanding oi our invention ref erence may bet had to.the accom anying: drawing wherein Fig l." is a somewhatdiag'ramrnaticelevation of a form of apparatus com prising' our invention; Fig. 2 is aplan view 0t the-Fig; 1- device; Figs: 3 and 4 are views,-'cor'res'p'ondii'1,,i to Figs; 1 and 2, of a modification and-Fig. 5 is aplanview oi a' furthermodification- I 3 The device shown in 'Figsll and21's generally similar to-that shown in Patent 2,44%),655 ofR; L.Keiiier andassigned' 'to the: same assignee as the present invention.v.The' glass: bulb or container I is supported vertically onthe upperend'iof a hollow head or holder 2 which may b'e-sup'por'ted bya bracket3 from a standard 4; The bulb l is additionally supported at its upperend by a suitable clip 5 extending from the standard 4. An innerelectrode in the form of a rod 6 having a pointed lower end is suitablymounted to extend axially within the bulb I and to be moved verticallytherethrough. The movement may be effected by means of a flexible cordor cable I connected to the upper end of the rod 6 and extending overpulleys 8 to a suitable winding drum or spindle.

The outer electrode is shown in the form of a stirrup having axes or legportions ill, ii] ex-- tending longitudinally along opposite sides ofthe bulb l and provided with a multiplicity of pointlike extensions Hthe tips of which are spaced 2. short distance from the wall of the bulbI. As here shown, the base portion of the stirrupshaped electrode 9 isprovided with a pulley l2 for rotation by a belt l3 from a suitabledrive, and is supported on a suitable bearing M attached to the holder2.

In carrying out the coating process, a smoke or gaseous suspension offinely divided particles of the fluorescent coating material is formedin any suitable generator such, for example, as that shown in theaforesaid patent to Keifler. The

smoke is introduced into the lower end of the bulb I through the hollowhead 2 so that it drifts upwardly along the bulb. The inner electrode 6is moved axially of the bulb, from the bottom to the top thereof, in thepath of the smoke. A difference of potential is maintained between theinner electrode 6 and the wall of the bulb I by applying ahigh D. C.potential (8,00012,000 volts, for example) between the inner electrode 6and outer electrode 9, the outer electrode being grounded. During themovement of the inner electrode 6, the outer electrode 9 is rotated andthe powder is uniformly electrostatically precipitated from the smokeonto the inner surface of the bulb I.

In the apparatus shown in Figs. 3 and 4, the

supporting structure for the bulb I and inner electrode 6 is like thatshown in Figs. 1 and 2 and corresponding parts have been similarlynumbered. However, in this case the outer electrode I5 is of relativelyshort axial length and is arranged tomove vertically along with theinner electrode 6. The electrode I5 is provided with a semi-cylindricalportion I6 having the point-like extensions I6 projectingrfrom its innersurface, and an upper annular portion I! to which is fixed a gear I8.The said gear. I8 meshes with a gear I9 which is driven by a motor 20.The assembly of electrode I5, gears I8 and I9 and motor 20 maybesuitably supported on a bracket or carriage 2| which is slidablymounted on the standard 4, and which may be moved vertically by a cordor cable 22 attached to the cord 1 by a cross member 23.

v The inner electrode 6 may be guided by one or more brackets 24 mountedon and electrically insulated from the standard 4.. The same arrangementmaybe employed in the apparatus shown in Figs. 1 and 2.

.It will be understood that upon the introduction of the smoke into thehead 2 of the Fig. 3 device, both the inner electrode 6 and the outerelectrode I5 are moved upward and the outer electrode is simultaneouslyrotated about the axis of the bulb I while maintaining a. difierence ofpotential between the electrodes to deposit the powder progressivelyalong the inner wall of the bulb I.

If desired, the outer electrode in either of the 4 arrangementsillustrated in Figs. 1 or 3 could be made cylindrical, as indicated at25 in Fig. 5. Also, provision may be made for rotating the bulb 6 aboutits axis as in the apparatus shown in the aforesaid patent to Keifier.It will be understood by those skilled in the art that the constructionand arrangement of parts may be widely modified within the spirit andscope of our invention as defined by the appended claim.

What we claim as new and desire to secure by Letters Patent of theUnited States is:

In apparatus for electrostatically coating tubular glass containers, thecombination of support means including holder means for the container,an inner electrode mounted on said support means to extend axially ofthe container, means including an outer electrode mounted on saidsupport means adjacent the outer wall of the container and arranged toeffectively present a multiplicity of discrete sharply pointedextensions uniformly over and projecting toward the wall of the saidcontainer, said outer electrode extending a limited distance axially ofthe container and being located adjacent an end of the inner electrode,means for moving said inner and outer electrodes in cooperative relationlongitudinally of the container and means for simultaneously rotatingsaid outer electrode about the axis of the container, means forconducting a gaseous suspension of finely divided coating material intothe container, and means for impressing upon said electrodes a potentialof sufiiciently high potential to cause deposition of said coatingmaterial upon the inner wall of said envelope.

WALTER ROY BLOOD. JAMES WILLIAM MOORE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES) PATENTS

